Archive for the ‘Workbench’ Category

Well, I had it wrong…the pin-outs were as the datasheets showed. But I had to actually draw a picture of the device (both top and bottom view) to convince myself of what I was seeing. Long story short, it works as it should and I am happy with the results.

Here is a pic of the PCB of the VFO and a pic of the output from T1 on my scope.

The power out at 13 MHz is 640 mv peak to peak and 412 mv at 32 MHz. I was surprised that the second harmonic was way down in the noise floor, barely noticeable.

Again, this as part of a project that Todd, VE7BPO proposed back in the winter months as a two part article for the Michigan QRP Club’s quarterly publication called the T5W. Todd did the first article that featured the divider portion of the project that follows this VFO. In a nutshell, the VFO produces a signal source from 13 to 31 MHz. The 20 meter segment is analog and the 40 and 80 meters segments are produced by the digital portions of the project by dividing the analog signal by two and four respectively.

This project was originally conceived by Wes, W7ZOI…and reproduced my many others to follow him. Though this project falls short in producing a lab grade signal generator, it does provide a great signal source for 3.5 to 30 MHz and can come in handy in the shack and on the workbench. My thanks to Todd for suggesting this project…I learned a lot and had a lot of fun getting there!

Well, I ran into a road block this afternoon that took some time to sort out. I built the FET VFO and Follower (for isolation) portions of the VFO…but could not get it to oscillate. After checking wiring and voltages, I pulled another 2N4416A from the junk box and checked it with my M-Cubed semiconductor checker. I noticed that it showed the DRAIN and SOURCE pins reversed from what the datasheet indicated. I rebuilt the two stages using the info that the M-Cubed checker showed me and the VFO worked. I got these 2N4416A’s from a reputable USA company but now wonder if maybe they were clones from an overseas location. Bottom line…never assume anything, always check and measure everything.

Have the BUFFER AMP to build and then do some tweaking and final measurements. This project is a joint effort of Todd, VE7BPO and myself for an article for the Michigan QRP Club’s quarterly publication called “The 5 Watter” (T5W). Todd suggested this article during the winter months and it has been a fun adventure so far. I sort of got side tracked this last month and just now am getting back on track with the project. The original 8640-jr project was done by Wes, W7ZOI…it is a three band VFO that develops a 13 to 30 MHz signal which is then ran through a couple of dividers to result in 3.5, 7 and 14 MHz VFO signal source or can be configured to run from 3.4 to 31 MHz as a signal generator.

Always fun to snuff solder fumes and figure out why things don’t work the first time as planned <smile>.

Started assembling a 8640-jr VFO tonight. Should have done this a month ago but been rather busy with no-related bench stuff lately. Built and tested the +6 volt strip and now onto the oscillator and buffer stages.

Located and sorted the parts for the entire project…now just need to build it, then test and measure the three stages. This is for a T5W article that VE7BPO inspired a couple of months ago.

Received the 4×20 (4 lines, 20 characters per line) LCDs. This made using the CW Decoder so much more enjoyable to use. I changed the code a bit to put the WPM rate and my call sign on the first line and then three lines of cw.

I need to take a picture of the setup now as it is easier to read the CW as it is displayed and then post it here on the blog.

Hello to Fred, KD8IXP. He is a local ham who is always bugging me about updating my blog. He just received two PIXIE transceiver boards, and has promised me to get on the air with one of them so I can hear what it sounds like. I will report back on this when he finally fulfills his promise!!!

Been doing some Arduino stuff on the workbench. I saw an article that used an Arduino for a CW Decoder. Built it but it didn’t show anything on the LCD. After some checking, realized that the schematic I was using and the software I had loaded onto the Aruduino didn’t match as far as LCD wiring. After some experimenting with various pin-out configurations, I ended up with a working cw decoder.

I also built up a breadboard for future Arduino experiments and prototyping. I have three books that I bought this last year that deals with Arduino projects and Ham Radio. This breadboard will be perfect for doing most of the experiments detailed in each of the three books.

I am also doing a VFO/Sig Gen project with Todd, VE7BPO. All of the project will be detailed in the Michigan QRP Club’s quarterly publication called the T5W. Todd is doing most of the work, and my part will only be the VFO section. It is based on a project done by Wes, W7ZOI in 2009. Called the 8640 –JR (a humorous namesake after the famous HP 8640 signal generator) this signal generator uses only 1 VFO but covers three ranges by applying HC74 series CMOS logic for frequency division.

That is it for now. Stay tuned for solder fume snuffing while the temps are chilly and the ground is white!

Wanted to mention what I found by comparing the molded inductor verse the use of a toroid for the RF Phase Shift.

Found that the molded inductor (molded inductor for the primary and four turns of hook-up wire for the secondary) has at least a 10 dBm loss at 7 MHz. I wound a toroid for the same component with ten turns for the primary and four turns for the secondary on a FT37-61 and had only a 2.8 dBm loss at 7 Mhz. So, using the toroid is the better choice. But, modeling this new insight with LTSpice still leaves me with some doubt. The RF level going into the Detector stage is still not up to 700mv which I think would be necessary for good sensitivity. I doubt I will continue on with this project in its present form. Still have some desire to use the LO ceramic osc and hook it up to a homebrew NE602/LM386 receiver I build a few years ago to see if that would work.

Have discovered some really interesting functions for LTSpice…things I wish I had known years ago. Still learning how to set-up sources for driving oscillators, mixers, etc and what types of analysis’s tell me what type of information. This learning has turned out to be more fun that I first imagined!

With the fourth just around the corner, I doubt I will get much done till next week. I have started to do the 30 meter mod for my KX1 and also want to do the auto tuner kit while I am in the kit building mood.

Been trying to use LTSpice with the binuaral receiver project. What I have learned is I am quite stupid when it comes to modelling a stage and understanding what is going on (using LTSpice). I have pestered a very patient friend from down under and I decided this morning that I should be able to answer some of the questions I have been throwing his way.

So, for the near future, I need to get a better handle on understanding and using LTSpice … then I can go back to modelling what I am doing before snuffing solder fumes. There is enough tutorial info out there on the web about LTSpice and how to make the best use of it…and I need to learn (relearn???…now I am wondering how much of it I learned the first time) LTSpice from a homebrewers point of view and how to make it a useful tool for me.

This is rather embarrassing to admit, but it is the truth and I really want to be able to use it (LTSpice) the way others have come to use it and learn from it.

Well, found that a bad scope probe can be a big problem when trying to understand things…LOL. Since replacing the bad probe, I discovered that the LO is working fine, have just over a volt coming out and going to the Product Detector. The RF input section still bothers me but it seems to be working as it should. However, the RF Phase Shift inductor (molded inductor) may be a problem, so after looking at things, I am going to take Mark’s advice and try a torroid. This may help recover some gain I seem to be losing. I get a three fold gain in voltage (317mv input/922mv output) from the RF Amp…but this varies as the input signal decreases in amplitude.

I have thought about incorporating some type of feedback for the RF Amp section to help maintain the RF level from the input to the Product Detector. I can hear a signal with -50 dBm input, but any less than that and I lose all AF going to a speaker/headphone. I should be able to use half that value of input signal and still hear a signal. I am thinking after I try swapping a torroid for the molded inductor, I may switch to a single signal type detector or pop a NE602 in-place of the current front end and see what I get. Since I wouldn’t be able to hear the binuaral effect anyway (due to being deaf in one ear), I might as well move on and try other ideas.

I built a 40 meter NE602 receiver a number of years ago and it was fun and simple. I may use the LO from this project and incorporate that receiver into a single signal receiver. I want to make up one 80 meter LO and one 40 meter LO on separate PCB boards to have on the bench for future use. All in all, this has been a fun and thought provoking exercise. I need to keep a focus on little things that can affect the overall success of the project (Thanks Mark of helping me learn this!), and remember to check my measurement methods to ensure they are sound and accurate.

I will probably have one more update after this and then move on to another project involving a remote terminal for my PHSNA.

Been wrapped up in a bunch of chores/Honey-Do’s/etc and haven’t had much time to spend at the bench. Finally got back at it tonight and rechecked some measurements I did earlier on the LO and RF portion of the receiver project…and they do not match what I had recorded earlier.

Since the forecast is for rain all day tomorrow, I hope to remeasure everything and re-evaluate what I have so far and where to go from here. Since I am deaf in one ear…making a binaural receiver makes little sense. Have been thinking of changing directions with this project since the LO was the main interest when I started this whole thing. Thinking of rewiring the front end and using a NE602 to see what that produces…and spend some more time with the current product detector to better understand it.

A special thanks goes out to Mark Dunning from down-under who has pointed out some items I overlooked…and in general made me reconsider just what I am doing and where I might go with this. Its always better to have an extra pair of eyes and a second opinion to help one focus on what they are doing!

Well, the signal level loss was not as bad as I first thought…but the ability to discern AF is not what I was hoping for. With a -40 dBm input signal level, the AF (in headphones) is just barely noticeable. Actually, from -35dBm input and lower, the AF is nearly useable.

I have post the signal level loss with a -3dBm input signal level to show the loss for the RF portion of the receiver to be about -7dBm (from input to product detector).